In the manufacture of semiconductor devices having submicron line widths, X-ray lithography is often used to replicate a desired pattern from a mask to a semiconductor wafer. Since different masks are used in different processing steps of the wafer, it is of critical importance that the alignment of each mask relative to the wafer be held to a very tight tolerance.
It is known in the prior art to use a combination of a piezoelectric element and a pivoting arm in a positioning device having a single degree of freedom as is shown in an article by Scire and Teague at pages 1735-40 of The Review Of Scientific Instruments, 49(12), December, 1978. In order to provide all six degrees of freedom (translation along, and rotation about, each of the X, Y and Z axes), alignment apparatus constructed according to the prior art have utilized series stacked stages in which each stage provides one or several independent degrees of freedom. Exemplary of such a stacked stage alignment apparatus is a five stage apparatus disclosed by Yamazaki et al at pages 987-991 of The Journal Of Vacuum Science Technology, 15(3), May/June 1978. Since the length of the structural loop between the mask and the wafer increases as the number of stages increases, the prior art stacked stage apparatus becomes more and more susceptible to external vibration as the number of stages increases.
McCoy et al, in U.S. patent application Ser. No. 469,154, now abandoned, disclose a single stage alignment apparatus capable of providing mask movement in only three degrees of freedom (translation along the X and Y axes and rotation about the Z axis). The McCoy, et al apparatus, shown in FIG. 1, uses four piezoelectric elements to support and move the mask.
In accordance with the illustrated preferred embodiment of the present invention, a single stage alignment apparatus provides six degrees of freedom of an X-ray mask relative to a semiconductor wafer. Since only a single stage is used the apparatus is smaller and lighter than a stacked stage apparatus with the result that the stiffness of the apparatus is increased and position control of the mask is improved. The apparatus comprises three flexure assemblies spaced equiangularly around a stage plate which supports the X-ray mask. Each flexure assembly includes a Z-axis piezoelectric transducer and horizontal and vertical flexures which allow the stage plate to move smoothly. Three piezoelectic transducers provide motion of the stage plate in the X-Y plane.